Ultrasound imaging is a medical imaging technique for imaging organs and soft tissues in a human body. Ultrasound imaging uses real time, non-invasive high frequency sound waves to produce a two-dimensional (2D) image and/or a three-dimensional (3D) image.
Ultrasound imaging may be helpful in evaluating the progression of labor and/or other fetal measurements by allowing examination of cervical dilation, fetal presentation, position, rotation, and descent. A prolonged second stage of labor is a type of dystocia, whereby the fetus has not been delivered within three hours in nulliparous women or two hours in multiparous women, after the cervix has become fully dilated. Women undergoing a prolonged second stage of labor typically need intervention, which involves instrumental delivery (using obstetric forceps or ventouse) or Cesarean section or failed instrumental delivery followed by Cesarean section.
In recent years, the rate of Cesarean section has increased dramatically. The failure to progress and fetal distress are the two most common indications for performing surgical deliveries or Cesarean section. Cesarean sections are associated with the risk of maternal morbidities such as bladder trauma and hematoma and unnecessary Cesarean sections are best avoided.
Currently, digital transvaginal examination of fetal descent is typically used to evaluate fetal head station and rotation, but this method is subjective and inaccurate with high interobserver variability. Recent studies have shown that ultrasound imaging might allow objective quantification of the level of fetal head descent in the birth canal. Multiple measurements have been proposed including the fetal head-perineum distance and measuring the ‘angle of progression’ (AOP) to evaluate the labor progress. With regard to AOP, it has been shown that the greater the AOP in the second stage of labor, the greater the probability of successful assisted or spontaneous delivery. Studies with fetuses in the direct occipitoanterior position have shown that the AOP correlates well with the decision to opt for spontaneous vaginal or instrumental delivery or Cesarean section. Although AOP may constitute a suitable, objective tool to evaluate progress of labor, AOP does not provide information regarding the fetal head rotation, which may also helpful in determining labor progress.
Specifically, as labor progresses, the fetal head rotates in a predictable way to fit through the pelvis. As discussed above, digital transvaginal examination of fetal head rotation can be unreliable. The position of the fetal head within the birth canal may be monitored with two-dimensional (2D) or three-dimensional (3D) ultrasound imaging. It is difficult and error prone, however, to determine the head orientation and/or rotation within a single plane of fetal descent when using 2D ultrasound imaging. Moreover, the use of 3D ultrasound imaging has its own challenges, such as needing a 3D ultrasound probe, having to register the 3D image data, and the ultrasound operator having to manually pick ultrasound slices for evaluation of head rotation (e.g., by determining the eye location), which can be difficult and tedious.
Other efforts for determining fetal head rotation include combining position tracking technology with advanced ultrasound imaging. For example, LABORPRO, which was developed by TRIG MEDICAL, maps the maternal pelvis by manually marking points on the pelvis or using a position sensor. This is followed by marking known fetal head landmarks on the ultrasound image. The two markings enable LABORPRO to determine the spatial position of the fetal head in relation to the pelvic bone, which may be tracked to provide fetal head rotation information. However, setting up and implementing the system in LABORPRO may be difficult in a chaotic atmosphere such as during labor.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.